The present invention generally relates to a technique for determining a storage device in a storage system.
In a financial institution or the like, for example, a large-scale storage system storing a vast amount of data ranging from several tens of terabytes to several tens of petabytes is employed. A disk array device employs a RAID (Redundant Array of Inexpensive Disks) is typically used as this type of storage system. A disk array device is capable of accommodating a plurality of storage media (between several hundred and several thousand storage media, for example).
Examples of storage medium types include a hard disk drive and a flash drive, for example. A flash drive is used to hold data in flash memory, but has an identical data input/output interface to that of a hard disk drive. Hence, a flash drive is interchangeable with a hard disk drive.
The performance of a storage medium varies according to the type and product model. As regards the storage medium type, for example, when a hard disk drive is compared to a flash drive, the data transfer speed during sequential access in a hard disk drive is greater than that of a flash drive. Depending on the product, however, this may not apply. More specifically, according to certain benchmarks, for example, a flash drive may have a data transfer performance that is comparable to sequential writing in a hard disk drive up to an I/O size (data transfer amount per I/O) of several kilobytes.
U.S. Pat. No. 5,920,884 discloses a method of increasing the speed of I/O processing by accessing flash memory components concurrently.
The power consumption of a flash drive is smaller than that of a hard disk drive, and it is therefore advantageous to use a flash drive as a data backup destination. U.S. Pat. No. 5,920,884 proposes a method of accessing flash memory components concurrently on the premise that access to a flash memory is slow. This premise is usually considered valid.
However, as described above, the performance of a flash drive is not always inferior to the performance of a hard disk drive. For example, with a configuration such as that of the method described in U.S. Pat. No. 5,920,884, in which a large number of flash drives are simply accessed concurrently, cases in which a high level of performance is not achieved may occur. An example of such a case is data copying executed using a copy function possessed by a disk array device. Data copying may take the form of copying performed within a single disk array device (so-called local copying) or copying performed from one disk array device to another disk array device (so-called remote copying), but in both cases it is considered difficult to achieve a sufficient level of reading performance in the copy source simply by employing the technique disclosed in U.S. Pat. No. 5,920,884.
The problem described above is not limited to a disk array device, and may exist similarly in other types of storage system.
Furthermore, in the case of copying, a copy source storage device may be set as a first storage device and a copy destination storage device may be set as a second storage device, but in other cases where the first storage device and second storage device are related, problems may occur even when it is possible to apply the technique disclosed in U.S. Pat. No. 5,920,884.